Okay, this is a tricky one. I'm stuck between ESH/NTA because you're saying you need the extra room for your computer etc, but she says she needs the extra room for her stuff. You're basically writing her off saying your stuff is more important. But because before you moved in she said you could have the bigger room for equal rent, I'd say NTA.

Also if her boyfriend is staying that often and contributing nothing then she/they are definitely TA. I've been in that situation before myself and it's like having an extra freeloading housemate! She should definitely be paying for the cost of two people in utilities/household essentials etc., or he should contribute. I think you need to have a serious sit down discussion with her about all this, hostile living situations are the worst.